The present invention relates to a method of producing an organic fertilizer and an organic feed by removing cadmium form processing residues of scallop, particularly to a method of producing an organic fertilizer and an organic feed by removing cadmium form processing residues of scallop in the condition of containing midgut gland where cadmium has been accumulated.
Over 500,000 tons of scallops are produced each year and they are important resources as food which account for approximately 10% of the total fish catch in Japan. The adductor muscle of a scallop which is a main edible part is only 15% weight of the whole scallop. The remaining shells (50% weight) and soft body part (35% weight) are discarded as processing waste. A large amount of useful ingredients such as protein and amino acid is contained in the soft body part and it is desirable that the useful ingredients are reused as fertilizers or feeds.
Hence, because of the biological concentration of up to 100 mg/kg of cadmium (Cd) in the midgut gland contained in the soft body part, the midgut gland cannot be reused as a fertilizer or a feed, and cannot be discarded as processing waste. Then, the present inventors have proposed means for removing the midgut gland from the soft body part, separating cadmium contained in the midgut gland, and reusing final residues of the midgut gland from which the cadmium is removed as organic fertilizers (see Patent Literature 1).
In the means described in Patent Literature 1, the midgut gland of scallop is removed from the soft body part, the midgut gland is ground with a mixer, 2% acetic acid solution in an amount equivalent to that of the midgut gland is added, the mixture is heated to 80° C. and stirred for 10 minutes, and the mixture is separated into solid residues and a cleaning liquid by centrifugation. Subsequently, 2% acetic acid solution of 2 times weight relative to the solid residues is added to the separated solid residues of the midgut gland, the mixture is heated to 80° C. and stirred for 10 minutes, and the mixture is separated into solid residues of the midgut gland and a cleaning liquid by centrifugation. Subsequently, the washing and separation operation is repeated twice. Then, final solid residues of the midgut gland thus washed are reused as organic fertilizers. The formed cleaning liquids are gathered and cadmium is separated and removed therefrom, and then the resultant solution is reused as a liquid organic fertilizer.